1. Field of the Invention
The present invention relates to a device and a method for forming a thermally sprayed coating on a face of a base material.
2. Description of the Related Art
A technique that an inner circumference face of a bore of an aluminum cylinder block is strengthened by thermally spraying a metal such as iron or the like onto the inner circumference face is known. There are vigorous research activities in the field of thermal spraying techniques. Especially intense research activities are being carried out on arc thermal spraying techniques, which allow cheap operating cost, to replace plasma thermal spraying techniques, in which operating cost is expensive. In the arc thermal spraying techniques, two wire-shaped thermal spraying materials, in which differing voltages are applied between the two wire-shaped thermal spraying materials, are delivered to a location where the tips of both are adjacent. Thereupon, an arc is generated between the tips, thus forming droplet of the thermal spraying material by the arc. An air current, for atomizing the droplet and scattering atomized droplets of the thermal spraying materials is directed towards a face to be thermally sprayed through the droplet. The air current atomizes the droplet into fine droplets and the atomized droplets are smashed and piled on the face to be thermally sprayed. The wire-shaped thermal spraying materials are delivered such that they can be maintained in a positional relationship in which their tips, which are being consumed, remain mutually adjacent. U.S. Pat. No. 6,091,042 issued to Benary teaches a technique in which an air current is propelled towards droplet formed in a region adjacent the tips of two thermal spraying materials and the atomized droplets are consequently smashed onto the face to form the thermal spraying coating.
In a case where an inner circumference of a bore or the like is to be thermally sprayed, thermal spraying must be performed such that an area of atomized droplets scattered onto the bore inner face moves along a circumferential direction of the inner circumference face of the bore. In the prior art, the thermal spraying device is fixed in position and the cylinder block is rotated so that the inner circumference face of the bore moves in a circumferential direction around the thermal spraying device.
The method of rotating the cylinder block has a problem that only one cylinder bore can be thermally sprayed at a time, and the thermal spraying process is consequently time consuming.
A technique to deal with this problem is set forth in U.S. Pat. No. 5,714,205 issued to Marantz et al. In this technique, the location in which the tips of the wire-shaped thermal spraying materials are adjacent is treated as a center, and a plurality of air current propelling nozzles is disposed around the center. Each of air current propelling nozzles propels an air current toward the center. By using the plurality of air current propelling nozzles disposed around the center, the direction of the air current can be made to rotate, for example, in a clockwise direction by activating one of the air current propelling nozzles sequentially in the clockwise direction. There is no need to rotate the cylinder block or the like with this technique. Further, there is also no need to rotate the thermal spraying device.